The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to antiparallel couple the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer).
The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer.
One on-going objective in the industry is to improve or increase the amount of data that can be stored on a disk and to design magnetic heads which can adequately read from and write data to these disks. One promising technique to increase the disk storage capacity is heat assisted magnetic recording (HAMR), which may also be referred to as optically-assisted magnetic recording or thermally-assisted magnetic recording. This technique utilizes a recording medium that has a higher coercivity than current media so that it has more resistance to thermal instability at normal operating temperatures. Therefore, more data can be adequately stored on the media. Unfortunately, a higher coercivity means that the platter tends to resist reacting to magnetic fields at typical operating temperatures. Therefore, it is difficult to write to such media using conventional read write heads. To sufficiently write data to high coercivity media, a disk drive needs to heat a writable portion of the disk to lower its coercivity as the write head writes data thereto.
Heat assisted magnetic recording systems use heating devices such as a laser or an electrically resistive heating element. This heating element is incorporated into the head near the read and write elements in order to heat the medium at the location at which the write element is writing. Circuitry for applying electrical power to the heating element is incorporated with the circuitry for the read and write elements. Generally a pair of leads connected with the read element are connected with read head pads located on a surface of the slider body. Similarly, a pair of leads connected with the write element connect with write head pads on the surface of the slider body. These pads are used to connect the read/write circuitry on the slider with leads on the suspension body that connect with pre-amp circuitry which may or may not be located on the suspension arm.
The use of a heating device, of course, requires its own circuitry in addition to that for the read and write heads. The heating device may also require an additional pair of pads on the surface of the slider. The circuitry for the read sensor, write element and the heating element, as well as the associated pads for each of these devices are all located on a single surface of the slider at the trailing end of the slider. As can be appreciated, limited space area on the trailing end of the slider, as well manufacturing considerations, require that the circuitry for each of these devices (read sensor, write element and heater) be located in close proximity to one another. In addition, the lines of circuitry for these devices must cross over one another at some point, the lines of circuitry being separated from one another by a dielectric material such as for example photoresist or alumina (Al2O3).
A problem that arises as a result of using such additional heating devices in a heat assisted recording system is that the heater leads, which must at some point cross the read sensor leads, cause capacitive interference with the read sensor. As voltage is applied to the heater leads during a write operation, capacitive coupling with the read sensor leads results in a voltage in the adjacent read sensor leads. This causes the read sensor to inadvertently detect the heater voltage as a signal resulting in signal noise of such a degree that the heat assisted head becomes inoperable.
Therefore, there is a strong felt need for a head design that can allow the use of an extra device such as a heater in a magnetic read write head while minimizing capacitive coupling between the extra device and the read sensor. Such a head design would preferably not involve additional costly manufacturing processes, and would preferably incorporate existing manufacturing materials and processes.